This invention relates generally to conveyor systems, and in particular to the induction section of a conveyor sortation system. The induction section of a conveyor system generally refers to the portion of the conveying system in which articles are inducted, or initiated, into the conveying sortation system. The induction section typically performs the function of providing the proper gaps between packages, or other articles traveling on the conveying system, so that the packages can be sorted for proper distribution. The proper gapping between articles on the conveying system is important for a variety of reasons. First, the gapping of the articles affects the throughput of the conveying system, which is often a factor of high commercial significance. By reducing the gaps between articles on the conveying system, the number of articles that can be placed on the conveying system at a given time is increased. By being able to place more articles on the conveying system at a given time, more articles are moved over a given time period, thus increasing the throughput of the conveying system.
Second, the gapping of the articles is highly important because the gapping affects the sortation functions of the conveying system. Where the conveying system functions to sort the articles being conveyed, prior art conveying systems have often used pusher shoes or other diverting means to push the articles off of a main conveyor onto one or more branch conveyors. In order for these pusher shoes to sort the packages correctly, it is important that sufficient space be provided between articles so that the pushers do not inadvertently push against another article while they are in the process of diverting a second article. Further, pusher shoes on some sorters tend to rotate the article, at least partially, when they are in the process of diverting the article onto a branch conveyor. This rotation ensures that the articles are properly aligned with the branch conveyor when they are diverted. In order for the article to be rotated, however, it is necessary for there to be a space behind the article in order to provide room for the rotation of the article. If insufficient space is allotted, the article may contact another article while being rotated, thus causing it to enter the branch conveyor misaligned, or to not be diverted at all.
The sortation functions of the conveying system therefore weigh in favor of providing a certain amount of gapping between articles while the throughput considerations weigh in favor of reducing this gapping to as small a space as possible. In order to best balance these competing interests, the induct portion of the conveying system would ideally be able to consistently and accurately produce gaps that were just large enough to accommodate the gapping requirements of the sortation section of the conveying system while rarely, if ever, exceeding these minimum gapping requirements. Prior art induct systems, however, have left room for improvement as to the consistency, accuracy, and speed at which at which gapping of the articles can be performed. Particularly as increases in throughput have been based on increasing conveyor speed while reducing gapping, the necessity for precise gapping in conveyor systems has increased.
One reason for the less than desirable performance of prior induct systems has been the inaccuracies that result in controlling an article as it transitions from one conveyor to another. Because gapping between articles can only be changed by changing the speed of one article with respect to another article, the creation and control of gaps tends to occur by utilizing at least two conveyors. For example, if an upstream conveyor is traveling at a first speed and a downstream conveyor is traveling at a different speed than the first conveyor, an article moving from the upstream conveyor to the downstream conveyor will increase the gap between it and any trailing package behind it as it passes onto the downstream conveyor. This increase in gap is due to the acceleration of the article as it initially arrives on the second conveyor. For a certain amount of time, the leading article is traveling at a higher speed (the speed of the downstream conveyor) than the trailing article, which is traveling at the speed of the upstream conveyor. This difference in speeds enlarges the gap between the two articles.
In the past, the controlling of gaps by using multiple conveyors traveling at different speeds has resulted in inaccuracies of the created gap partially because the point at which an article switches from having its speed controlled by the upstream conveyor to the downstream conveyor has not been able to be accurately determined. While this point is often assumed to correspond to the moment when the center of gravity of the article reaches the midpoint between the upstream and the downstream conveyors, this assumption often proves incorrect, thus leading to inaccuracies in the created gaps.
The creation of gaps in prior art conveying systems has also been inaccurate because these prior art conveying systems are not able to accurately determine the position of articles on the conveyors. For example, in some prior art conveying systems, the position of the article was determined by sensing the passing of the article by a single photo-detector positioned alongside the conveyor. As the article moved past the single photo-detector, its position was computed by computing how far the conveyor belt had moved since the article had been detected. Determining how far the conveyor belt had moved often was carried out by way of an encoder that measured the amount of rotations of the motor that powered the conveyor belt. Due to measurement inaccuracies, slippage, and other factors, this calculation of the article""s position on the conveyor has a significant uncertainty. This uncertainty of the article""s position on the conveyor makes controlling the created gaps in prior art induct systems difficult.
In light of the foregoing disadvantages of the prior art, the need for an induct system that improves the accuracy and consistency of the created gaps between articles can therefore be seen.
Accordingly, the present invention provides an improved method and apparatus for inducting articles into a conveying system. The method and apparatus allow the position of articles traveling on individual conveyors to be more accurately determined, thus aiding the accuracy and precision of the gapping process. The method and apparatus of the present invention also allow an accurate determination, rather than an assumption, to be made as to the point at which an article moving from one conveyor to another changes from having its speed controlled by the upstream conveyor to that of the downstream conveyor.
According to one aspect of the present invention, a method is provided for determining the control point of an article traveling on a conveyor system. The method includes providing a first and a second conveyor. The first conveyor includes a downstream end that is aligned with an upstream end of the second conveyor. The method further includes detecting when a change occurs in the speed of the article due to the article having reached the second conveyor. According to another aspect of the present invention, a method for controlling a gap between a first and a second article on a conveyor is provided. The method includes providing a first and a second conveyor which are aligned with each other. The speed of the second conveyor is set to be different than the speed of the first conveyor. The control point of the first article is measured as the first article passes from the first conveyor to the second conveyor. Any gap between the first article and the second article is measured while the first article is traveling at least partially on an adjustable speed conveyor. The measured gap is compared to a desired gap, and the speed of the adjustable speed conveyor is adjusted in order to reduce any difference between said measured gap and said desired gap.
According to still another aspect of the present invention, a method is provided for creating a gap between a first article and a second article. The method includes providing a first and a second conveyor which are aligned with each other. The first conveyor is an adjustable speed conveyor. Any gap between the first and the second article is repetitively measured while the first article is at least partially positioned on the first conveyor. Any difference between the measured gap and a desired gap is calculated. A feedback controller is provided which takes the difference between the measured gap and the desired gap and outputs a command for adjusting the speed of the adjustable speed conveyor. The outputted command is based upon the difference between the measured gap and the desired gap.
According to still further aspects of the present invention, apparatuses for carrying out the above-described methods are provided. The measuring of the gap between articles may be accomplished by way of a horizontal array of photo-detectors. The determination of the control point of an article may also be carried out by way of a horizontal array of photo-detectors. The determination of the size of a gap, as well as the issuance of a speed command based upon the size of that gap, may also be repeated multiple times for an individual gap. In this manner, direct feedback is provided to the speed controller for the adjustable speed conveyor as the gap is either maintained or changed. The feedback controller may be a proportional-integral-derivative type controller. In still further aspects of the present invention, the methods and apparatuses for determining the control point of an article can be combined with, or utilized separately from, the methods and apparatuses for creating a gap.
The methods and apparatuses of the present invention provide an improved induction system that allows gaps to be created between packages that are more accurate and consistent, as well as allowing the induction system to operate at higher speeds while maintaining this improved accuracy and consistency. These and other advantages of the present invention will be apparent to one skilled in the art in light of the following specification when read in conjunction with the accompanying drawings.